ERV global pressure demand control ventilation mode

ABSTRACT

An energy recovery ventilator includes first and second blowers, a pressure transducer and a controller. The first blower is configured to direct a first air stream into a first zone of an enclosure. A second blower configured to direct a second air stream into a second zone of the enclosure. A pressure transducer is configured to determine internal air pressure within the enclosure. A controller is configured to control the first blower and/or the second blower in response to the internal air pressure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to U.S. application Ser. No. 13/267,542 toJustin McKie, et al. and U.S. application Ser. No. 13/267,441 to JustinMcKie, et al. both filed on even date herewith, and both commonlyassigned with this application and incorporated herein by reference.

TECHNICAL FIELD

This application is directed, in general, to climate control systems,and, more specifically, to methods and systems for improving operatingefficiency of such system.

BACKGROUND

Some HVAC units are located on the rooftop of a commercial building.These so-called rooftop units, or RTUs, typically include one or moreblowers and heat exchangers to heat and/or cool the building, andbaffles to control the flow of air within the RTU.

One aspect of airflow control is the venting of stale air within thebuilding and the intake of fresh air from the outside to maintain airquality within the building. This exchange of air is a significantpotential source of energy loss, as fresh air may need to be cooled orheated to maintain the temperature set point in the building, andpreviously cooled or heated air is lost to the environment.

The loss of energy that results from air exchange is a source ofpotential savings in the continuing effort to improve efficiency ofcommercial HVAC systems.

SUMMARY

One embodiment provides an energy recovery ventilator that includesfirst and second blowers, a pressure transducer and a controller. Thefirst blower is configured to direct a first air stream into a firstzone of an enclosure. A second blower is configured to direct a secondair stream into a second zone of the enclosure. A pressure transducer isconfigured to determine internal air pressure within the enclosure. Acontroller is configured to control the first blower and/or the secondblower in response to the internal air pressure.

Another embodiment provides a method, e.g. for manufacturing an HVACenergy recovery ventilator. The method includes configuring first andsecond blowers, a pressure transducer, and a controller. The firstblower is configured to direct a first airstream into an enclosure. Thesecond blower is configured to direct a second airstream from saidenclosure. The pressure transducer is configured to determine aninternal air pressure within said enclosure. The controller isconfigured to control one or both of said first and second blowers inresponse to said internal air pressure.

Yet another embodiment provides an HVAC energy recovery ventilatorcontroller. The controller includes a processor, input and outputinterfaces and a memory bearing processor instructions. The inputinterface is configured to receive and convert a pressure signal from apressure transducer to a form readable by said processor. The outputinterface is configured to convert a blower control signal from saidprocessor to a form suitable to control a blower. The memory isconfigured to direct said processor to control said blower in responseto said pressure signal.

BRIEF DESCRIPTION

Reference is now made to the following descriptions taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 illustrates an HVAC system according to one embodiment, includinga roof-top unit and an energy recovery ventilator (ERV) configured tomaintain an internal pressure set point;

FIG. 2 illustrates an ERV controller configured to control one or moreERV blowers to maintain an ERV internal pressure set point;

FIG. 3 is an operation flow chart for one embodiment of the ERVcontroller of FIG. 2;

FIG. 4 illustrates pressure as a function of flow rate in one embodimentof an ERV configured to maintain an internal pressure set point, e.g. inzone II of the ERV of FIG. 1; and

FIG. 5 is one embodiment of a method of manufacturing the HVAC system ofFIG. 1.

DETAILED DESCRIPTION

Many commercial buildings provide heating and cooling with a roof-topheating, ventilating and air conditioning (HVAC) unit, or RTU. Some suchsystems include an air-side economizer, or briefly, an economizer. Theeconomizer provides the ability to selectively provide fresh outside airto the RTU or to recirculate exhaust air from the building back throughthe RTU to be cooled or heated again.

The HVAC system typically recirculates a portion of the exhaust air asit heats or cools the air. When the enthalpy of the fresh air is lessthan the enthalpy of the recirculated air, conditioning the fresh airmay be more energy-efficient than conditioning the recirculated air. Inthis case the economizer may exhaust a portion of the stale air andreplace the vented air with outside air. When the outside air is bothsufficiently cool and sufficiently dry it may be possible that noadditional conditioning of the outside air is needed. In this case theeconomizer may draw a sufficient quantity of outside air into thebuilding to provide all the needed cooling.

In some installations an energy recovery ventilator (ERV) may be used topre-condition the fresh air demanded by the RTU. The ERV may include,e.g. an enthalpy wheel to transfer heat and/or humidity between anincoming fresh air stream and an outgoing exhaust air stream.

In some cases difficulties may arise when balancing the fresh airrequired by the economizer and the fresh air provided by the ERV. Aconventional approach to such balancing might utilize some form ofcommunication between the ERV and the economizer. However, there areseveral reasons why such an approach may be undesirable. First, suchcommunication typically involves additional cost related to additionalinterfacing components, such as cables and wiring blocks. Second, somestandardization might be needed to allow for various models of the ERVto interface to various models of the RTU. Such standardization involvesadditional infrastructure complexity, such as interface standards.Third, such an interface represents a potential source of failure in theHVAC system, likely requiring inspection and maintenance.

To avoid such deficiencies of such conventional approaches, theinventors have discovered an innovative solution that allows the ERV tooperate cooperatively with the economizer RTU, while remainingelectrically autonomous of the RTU, by monitoring the pressure withinthe ERV. This scheme is sometimes referred to herein as Global PressureDemand Control (GPDC) ventilation mode. In various embodiments describedbelow, when the ERV operates in GPDC mode, the air flow within the ERVis controlled to maintain the pressure within the ERV at about the samelevel as the outside air, or atmospheric, pressure. When operated inthis manner the ERV becomes essentially invisible to the economizer, andthe fresh air requirements of the economizer are met without electricalcommunication between the ERV and the economizer. No interface betweenthe ERV and the economizer is needed, thus obviating the need forhardware and interface standards to implement the interface.

Turning to FIG. 1, illustrated is an HVAC system 100 according to oneembodiment. The system 100 includes an ERV 105 and an RTU 110. While theembodiment of the system 100 is discussed in the context of a roof-topunit, the scope of the disclosure includes other HVAC applications thatare not roof-top mounted.

The ERV 105 includes an enclosure (e.g. a cabinet) 112, first and secondvariable speed blowers 115 and 120, an enthalpy wheel 125 and a divider130. The blowers 115, 120 may be of any conventional or novel type, suchas radial or axial, impeller- or propeller-types. The blowers 115 and120 as illustrated are configured in a pull-pull configuration, butembodiments of the system 100 are not limited thereto. The enthalpywheel 125 may also be conventional or novel. Without limitation to anyparticular type of enthalpy wheel, those skilled in the pertinent artwill appreciate that enthalpy wheels typically include a heat and/ormoisture transfer medium that provides a semi-permeable barrier toairflow therethrough.

In the illustrated embodiment the enthalpy wheel 125 and the divider 130divide the ERV 105 into four zones, I, II, III and IV. The blower 115operates to draw an airstream 135 a from outside the enclosure 112 intozone I. The incoming air may be, e.g. outside air. As used hereinoutside air is air that is initially external to the ERV 105 and anenclosed space (such as a building) that is environmentally conditionedby the system 100. The air stream 135 a passes through the enthalpywheel 125 and enters zone II. Air within zone II may exit the ERV 105via an unreferenced outlet as an airstream 135 b.

The ERV 105 receives an air stream 140 a from the RTU 110 into zone III.The blower 120 draws the airstream 140 a through the enthalpy wheel 125to zone IV. The air exits zone IV via an unreferenced outlet.

In some embodiments the airstreams 135 a,b and 140 a,b all have about anequal flow rate, e.g. m³/minute. In some other embodiments the ERV 105includes one or more bypass dampers 150 that provide a controllable pathbetween one or more of the zones and the outside air. In such cases theair streams 135 a,b and 140 a,b may have different flow rates to reflectair that is drawn into or vented via the one or more dampers 150. In thefollowing description it is assumed without limitation for the purposeof discussion that any such dampers are closed so that the airstreams135 a,b and 140 a,b are about equal.

In the illustrated embodiment the ERV 105 is joined to the RTU 110 suchthat the ERV 105 provides the air stream 135 b to an unreferenced intakeof the RTU 110. The ERV 105 also receives the air stream 140 a from theRTU 110 via an unreferenced exhaust outlet of the RTU 110.

The RTU 110 includes an economizer 155, a cooling element 160, a heatingelement 165 and a blower 170. The blower operates to force an air stream175 into the building being conditioned via an unreferenced supply duct.A return airstream 180 from the building enters the RTU 110 at anunreferenced return duct.

A first portion 185 of the air stream 180 recirculates through theeconomizer 155 and joins the air stream 135 b to provide supply air tothe building. A second portion of the air stream 180 is the air stream140 a, which enters zone III of the ERV 105.

The economizer 155 may operate conventionally to vent a portion of thereturn air 180 and replace the vented portion with the air stream 135 b.Thus air quality characteristics such as CO₂ concentration and humiditymay be maintained within defined limits within the building beingconditioned.

If the airflow required to meet the demand of the economizer 155increases without a commensurate increase of the speed of the blower115, the pressure within zone II will decrease. A pressure transducer190 creates an electrical signal related to the pressure within zone IIand sends the signal to a controller 195. The controller 195 thenincreases the speed of the blower 115 to increase the pressure withinzone II. The controller may also increase the speed of the blower 120 toincrease the flow of the air stream 140 a. Thus the fresh air supplydemanded by the economizer 155 may be met without electricalcommunication between the RTU 110 and the ERV 105.

Analogously, the economizer in some cases may reduce its demand forfresh air, recirculating a greater portion of the air stream 180 to theconditioned building. In this case the pressure in zone II is expectedto increase without a commensurate reduction of the blower 115 speed.The controller 195 can then reduce the speed of the blower 115 to allowthe pressure in zone II to decrease. The controller 195 may also controlthe speed of the blower 120 to match the flow of the air streams 135 band 140 a. Thus, the fresh air requirement of the economizer 155 may bemet.

In some embodiments the fans 115, 120 may be configured in a push-pushconfiguration. In such embodiments, the fan 115 may be located at thefresh air inlet to zone I of the ERV 105. The fan 120 may be located atthe inlet to zone III. As previously described, when the fresh airdemand by the economizer 155 increases the pressure in zone II isexpected to drop without an increase in fan speed, and when the freshair demand decreases the pressure in zone II is expected to increase.Thus the pressure transducer 190 may be located in zone II in suchembodiments to communicate the pressure within zone II to the controller195. The controller 195 may control the fans 115, 120 as previouslydescribed to maintain the pressure within the zone II at about zero.

FIG. 2 illustrates aspects of the controller 195 and its relationship tothe pressure transducer 190 and the blowers 115, 120. The controller 195includes a processor 210, a memory 220, an input interface 230 and anoutput interface 240. The processor 210 may be any type of processor orstate machine suited to electronic control systems. The processor 210may be analog or digital, and is described without limitation as adigital controller. In an illustrative example, without limitationthereto, the processor 210 is a commercially available microcontroller.

The memory 220 stores operating instructions for the processor 210. Theoperating instructions include instructions to implement the controlfunctions that operate the system 100 according to various embodimentsdescribed herein. The memory may also include various instructionsrelated to general operation of the system 100 unrelated to the ERV 105.The memory 220 may include one or more electronic components distinctfrom the processor 210, or may be partially or wholly embedded withinthe processor 210.

The input interface 230 is configured to convert an electrical outputfrom the pressure transducer 190 to a form that is readable by theprocessor 210. The interface 230 may include any type of conversiondevices, such as without limitation an analog-to-digital converter(ADC), current to voltage converter, voltage to current converter, oramplifier. In some embodiments the interface 230 is partially or whollyembedded within the processor 210.

The output interface 240 is configured to convert an electrical outputfrom the controller 210 to a form that the blowers 115 and 120 areconfigured to recognize as control signals. For example, the outputinterface 240 may produce a DC voltage proportional to a desired blowerspeed. The interface 240 may include any type of conversion devices,such as without limitation a digital-to-analog converter (DAC), currentto voltage converter, voltage to current converter, or amplifier. Insome embodiments the interface 240 is partially or wholly embeddedwithin the processor 210.

In various embodiments the pressure transducer 190 reports an absolutepressure of the zone within which it is located. The controller 195 maybe configured to control the fans 115, 120 to maintain an absolutepressure set point that is stored in the memory 220 or otherwisecommunicated to the controller 195. In other embodiments the controllerdetermines a differential pressure ΔP between the pressure reported bythe pressure transducer 190 and the outside air. The outside airpressure value may be stored as a static value or may optionally bedetermined by a second pressure transducer (not shown). Various aspectsof this discussion may refer to the controller 195 operating to maintainΔP at about zero. However, the scope of the disclosure explicitlyincludes embodiments in which the controller operates to maintain aparticular non-zero pressure set point.

FIG. 3 illustrates one embodiment of a method 300 for controlling theoperation of the system 100. The method 300 may be implemented ininstructions stored by the memory 220. In various embodiments, includingthat illustrated by FIG. 3, the method 300 is a subroutine of a moregeneral control algorithm configured to operate the system 100, an inparticular the ERV 105. The method 300 is described without limitationwith reference to the controller 195, and more specifically to theprocessor 210. The method 300 is also described without limitation forthe case that the ERV 105 is configured in a pull-pull configuration.Those skilled in the pertinent art may modify the method 300 for thepush-push configuration.

The method 300 begins with an entry point 310 from a calling routine. Ina step 310 the processor determines if GPDC mode is active. The GPDCmode may be inactive, e.g. if the purchaser of the ERV 105 has notpurchased the GPDC option. If the GPDC mode is not active, the method300 returns to the calling routine via an exit point 399.

In the event that the GPDC mode is active the method 300 advances to adecisional step 320. In the step 320 the processor 210 determines if thepressure differential reported by the transducer 190 is about equal to adesired set point, e.g. zero. In making this determination, theprocessor 210 may employ various control features such as a guard bandor hysteresis to avoid over-controlling the ERV 105. If the pressure isabout zero, the method 300 exits at the step 399.

In the event that the pressure is not about zero, the method 300advances to a decisional step 330. If the reported pressure differentialis greater than about zero, the method advances to a step 340. In thestep 340 the processor outputs a signal to decrease the speed of blower115.

The method 300 then advances to a step 350 in which the speed of theblower 120 is adjusted. For example, the exhaust blower 120 may beadjusted to maintain a ratio of intake to exhaust air so that theinternal static pressure of the building being heated or cooled remainsabout constant. The method 300 then exits via the step 399.

In some cases it may be preferred that the speed of both of the blowers115 and 120 is decreased about equally. In other cases, such as when abypass damper is open in the ERV 105, the speed of the blowers 115, 120may be decreased unequally, or one blower may be unaffected.

In the event that in the step 330 the pressure is not greater than aboutzero, the method advances to a step 360. In the step 360 the processor210 outputs a signal to increase the speed of the blower 115.

The method 300 then advances to a step 370 in which the speed of theexhaust blower 120 is adjusted. As previously described, the speed ofthe blower 120 may be adjusted to maintain the static pressure of thebuilding being heated or cooled. Also as before, the speed of one blower15, 120 may be adjusted differently then the other blower or not at all.The method 300 then exits via the step 399.

FIG. 4 illustrates a relationship, in one illustrative and nonlimitingembodiment, between the rate of outside air flow, e.g. the airstream 135b, and the pressure upstream of the economizer damper as measured by thepressure transducer 190 of the ERV 105. In this embodiment the pressuretransducer 190 was located in zone II of the ERV 105 in a pull-pullconfiguration. The pressure characteristic includes a portion thatdecreases about linearly with increasing intake airflow. Thus within thelinear region it is expected that a control algorithm configured tomaintain a pressure set point within the ERV 105, e.g. the method 300,will be well-behaved. Some air quality regulations require that freshair be controlled to within 15% tolerance of a desired set point duringoperation of the RTU 110. The linear characteristic of the illustratedrelationship indicates that the required tolerance can be achieved witha system that is able to accurately measure pressure to 0.1 inch watercolumn. Thus embodiments of the system 100 are expected to comply withsuch regulations using GPDC, e.g. without electrical communicationbetween the ERV 105 and the RTU 110.

In some embodiments an operating setpoint 410 for the pressure measuredby the transducer 190 may be set at about a mid-range of the linearportion of the flow rate characteristic of FIG. 4. While the system 100may be operated such that the setpoint 410 is located at other than amidpoint of the flow rate characteristic, it is expected that variouscontrol algorithms may be more stable when the operating setpoint isconfigured as illustrated.

Turning to FIG. 5, a method 500 is presented according to one embodimentof the disclosure, e.g. a method of manufacturing an HVAC system. Themethod 500 is described in some cases by reference to various featurespreviously described herein, e.g. in FIGS. 1-3, without limitationthereto. Various embodiments of the disclosure may use some or all ofthe illustrated steps, and may include steps that are not illustrated.Furthermore, in some embodiments steps of the method 500 may beperformed in an order other than the illustrated order.

In a step 510 a first fan, e.g. fan 115, is configured to direct a firstairstream into an enclosure. In a step 520, a second fan, e.g. the fan120, is configured to direct a second airstream from the enclosure. In astep 530 a pressure transducer, e.g. the transducer 190, is configuredto determine an internal air pressure within the enclosure. In a step540 a controller, e.g. the controller 195, is configured to control oneor both of the first and second fans in response to the internal airpressure.

In a step 550 the controller is configured to control one or both of thefirst and second fans to maintain a pressure differential of about zerobetween an interior region of the enclosure and outside air pressure. Ina step 560 the first and second fans are configured in a pull-pullconfiguration. In a step 570 the energy recovery ventilator isconfigured to provide an input air stream to a rooftop HVAC unit.

Those skilled in the art to which this application relates willappreciate that other and further additions, deletions, substitutionsand modifications may be made to the described embodiments.

What is claimed is:
 1. An energy recovery ventilator (ERV) coupled to aneconomizer, comprising: an ERV housing including a divider and anenthalpy wheel that divides said ERV housing into multiple zones; afirst blower located within said ERV housing to force a first air streamthrough said enthalpy wheel and into of one of said multiple zones andout of said ERV housing; a second blower located within said ERV housingto force a second air stream into another of said multiple zones of saidERV housing and through said enthalpy wheel and out of said ERV housing;a pressure transducer located within said ERV housing and configured todetermine an internal air pressure within said ERV housing; and acontroller coupled to said pressure transducer to receive an electricalsignal therefrom and configured to control said first blower and/or saidsecond blower in response to said internal air pressure to maintainabout a same level of pressure within said ERV housing as an airpressure outside said ERV housing, thereby allowing the ERV to operatecooperatively with the economizer while remaining electricallyautonomous.
 2. The energy recovery ventilator as recited in claim 1,wherein said controller controls said first blower and/or said secondblower to maintain a pressure differential of about zero between saidinternal air pressure and atmospheric air pressure.
 3. The as recited inclaim 1, wherein said controller is configured to increase a speed ofsaid first blower and/or said second blower when said internal airpressure is less than an air pressure outside said enclosure.
 4. The asrecited in claim 1, wherein said controller is configured to decrease aspeed of said first blower and/or said second blower when said internalair pressure is greater than an atmospheric air pressure.
 5. The energyrecovery ventilator as recited in claim 1, wherein said is ERV housingis coupled to a roof top unit (RTU) housing to provide said firstairstream to an intake of said RTU housing.
 6. The energy recoveryventilator as recited in claim 1, wherein said pressure transducer isconfigured to determine an air pressure within a second zone of saidmultiple zones.
 7. The energy recovery ventilator as recited in claim 1,wherein said first and second blowers are configured in a pull-pullconfiguration, such that they direct air flow through said ERV housingin opposite directions.
 8. A method of manufacturing an HVAC energyrecovery ventilator for coupling to an economizer, comprising:fabricating an ERV housing including a divider and an enthalpy wheelthat divides said ERV housing into multiple zones; locating a firstblower in said ERV housing to force a first airstream through saidenthalpy wheel and into one of said multiple zone and out from said ERVhousing; locating a second blower in said ERV housing to force a secondairstream into said ERV housing through said enthalpy wheel and intoanother of said multiple zones and out of said ERV housing; locating apressure transducer in said ERV housing and configuring said pressuretransducer to determine an internal air pressure within said ERVhousing; and coupling a controller to said pressure transducer toreceive an electrical signal therefrom, said controller being configuredto control one or both of said first and second blowers in response tosaid internal air pressure to maintain about a same level of pressurewithin said ERV housing as an air pressure outside said ERV housing,thereby allowing the ERV to operate cooperatively with the economizerwhile remaining electrically autonomous.
 9. The method as recited inclaim 8, further comprising configuring said controller to control oneor both of said first and second blowers to maintain a pressuredifferential of about zero between said internal air pressure andatmospheric air pressure.
 10. The method as recited in claim 8, whereinsaid controller is configured to increase a speed of said first blowerwhen said internal air pressure is less than an external air pressure.11. The method as recited in claim 8, wherein said controller isconfigured to decrease a speed of said first blower when said internalair pressure is greater than an atmospheric air pressure.
 12. The methodas recited in claim 8, wherein said controller is configured to adjust adecrease a speed of said first blower when said internal air pressure isgreater than an external air pressure.
 13. The method as recited inclaim 8, wherein said pressure is determined in a zone of said enclosurelocated between a supply air outlet and said enthalpy wheel.
 14. Themethod as recited in claim 8, further comprising configuring said firstand second blowers in a pull-pull configuration, such that they directair flow through said ERV housing in opposite directions.
 15. The methodas recited in claim 8, further comprising configuring the energyrecovery ventilator to provide an input air stream to a rooftop HVACunit.